Chapter VI: Roasting and Glazing

Coffee undergoes essential chemical changes in the process of roasting. In the raw or natural state the coffee-bean is tough and horny in structure and entirely devoid of the appearance, character and peculiar aroma that so distinguishes it in the roasted condition, and by which it is best known to the public. The testa or investing membrane of the raw bean has a layer of long cells with a peculiar pitted structure, containing a crystaline substance chemically termed _Caffeine_, and another known as _Caffeic_, or tannic acid, while the inner substance consists of an assemblage of vesicles of an angular form, the cavities of which include in the form of little drops a considerable quantity of a highly aromatic oil technically termed _Caffeone_, on the presence and amount of which the fragrance and active principles of the coffee depends, and by which its commercial value in the roasted state is estimated. The existence of this “coffee oil” makes itself known in a striking manner by roasting; being driven out of the beans by the intense heat, it is partially volatilized and, together with other products of the roasting, produces the characteristic aroma peculiar to roasted coffee, an odor possessed by no other known substance. In the operation of roasting the beans swell up and open at the furrow by the liberation of the gases within their substance, their weight decreasing, but volume increasing in proportion to the extent to which the operation is carried, developing the aromatic oil and liberating at the same time a portion of the caffeine from its combination with the caffeic or tannic acid. The amount of this aromatic oil contained in coffee varies from 8 to 13 per cent. at least, one-half of which is lost by evaporation during the roasting process, so that it may prove a paying experiment to attempt to collect it, especially in large establishments where large quantities of coffee are roasted and several pounds of this valuable oil are dissipated daily, which would no doubt find a ready market at a good profit for the making of liqueurs, or medicinal use.

Before being roasted coffee also contains from 6 to 8 per cent. of sugar, which after roasting is reduced to as low as 1 per cent. and sometimes even to zero, from which it would appear that the description of sugar (cane) present in the raw coffee suffers destruction during roasting, which, however, is not the case, as in the process of roasting the saccharine matter in the raw bean is converted into caramel. A change in the fat of the raw coffee is also brought about by the roasting, for where ether extracts only some four to five parts of fat from the raw coffee beans, it readily extracts double that quantity from the roasted beans. So striking is this fact that Von Bibra has even credited the roasting process with the production of fat, whereas the action is only mechanical in bursting the fat-cells of the raw bean, thereby rendering the fat accessible to the solvent action of the ether.

The operation of roasting also tends to make coffee soluble in boiling water, as when raw coffee is perfectly exhausted by means of boiling water, it yields up only 25 per cent. which passes into solution, while roasted coffee, on the other hand, when completely exhausted by means of boiling water yields readily upwards of 40 per cent. of soluble matter, proving that in actually using coffee as a beverage, we are not in the habit of making anything like a complete extraction, as only some 10 to 12 per cent. of the active principles of the coffee passes into the liquid.

The modern appliances for the roasting of coffee are numerous and labor-saving to a great extent, many of them are, however, calculated only to enhance the appearance of the bean, while others enable the roaster to obtain almost to perfection the full development of the aromatic properties of the coffee. Coffee is roasted for commercial purposes and domestic use in a large sheet-steel or malleable-iron cylinder mounted on a hollow axle, so as to revolve over a brisk fire and allow the gases generated during the torrefaction to escape. The surface of the cylinder is perforated with a number of small holes for the purpose of allowing the vapor arising from the coffee in the process of roasting to pass off readily, and through the interior runs laterally four ridges, the object of which is to toss it about in all directions, causing it to pass from end to end, and diffuse a uniform heat to every part of the coffee in order to make the “roast” even and regular in appearance. This cylinder is again encased in a frame brick-work at the bottom of which is built a coal fire well distributed so as to heat all portions of the cylinder at the same time during the operation. On the outer head it has a small opening through which the operator occasionally inserts a “tryer” to enable him to note the progress made as the process advances, the cylinder being also so arranged that it can be drawn from over the fire when it is required to either fill or empty it through a slide or hopper in the centre. It is operated by steam-power, revolving slowly but regularly, and having a capacity of from 25 to 300 pounds.

After roasting, the coffee is run off into a large wire-bottomed box termed a “cooler,” to the end of which is fitted a powerful fan or “blower” used for forcing cold air through the hot beans and preventing the volatile oil from exuding, the coffee being thoroughly agitated during the process, the hulls, chaff and stems being removed meantime to a large extent by the fan and sieve. Thirty-five to forty-five minutes is usually the time consumed in the operation, the former for a “Light” and the latter for a high or “Dark” roast, the entire process of roasting, cooling and rebagging occupying about one hour. In roasting, coffee loses in weight from 12 to 16 per cent., according to the age and nature of the coffee under treatment and the extent to which the operation is carried, the average, however, being 14 per cent. for old and well-seasoned coffee, which accounts for the relatively higher price--three to six cents per pound--of roasted coffees, according to the price green and the loss per cent. in roasting. But, it at the same time increases in bulk--100 volumes of raw coffee yielding from 150 to 160 volumes of roasted--that is, two pints of raw beans will yield three pints roasted. It also loses from 1 to 2 per cent. more in the warm months of summer than in the damp months of winter, for which reason it should not be roasted as high in the former season as in the latter, owing to its greater tendency to sweat and absorb the higher temperature, thus causing the volatile oil to exude, and dissipate and impart an astringent taste to the infusion. When coffee is roasted light-brown, or until it assumes a pale-chestnut color, the loss is from 13 to 14 per cent. the quantity of extract obtained from such roast by means of boiling water ranging from 20 to 21 per cent. of the weight, while the loss in weight of the extract will be much larger if the roasting process is continued until the color becomes dark-brown or black by over-roasting. New, moist and light coffees lose a larger percentage than old, dry and solid ones, the average being about 14 per cent. The operation of roasting coffee is one of the greatest exactness, amounting almost to an art, perfect roasting requiring not alone skill and judgment but experience and constant practice, as not only the style, strength and flavor but also the commercial value of the coffee depends upon the operator deciding when it is properly parched or roasted. It is also one of a crucial nature, for equally by insufficient as well as by excessive roasting, much of the aroma of the infusion is lost, the beverage under either of these circumstances being neither agreeable to the palate or exhilarating in its influence. The operator, for these reasons, must judge of the exact amount of heat required for the adequate roasting of the different varieties, which, while variable, the range of roasting temperature proper for roasting the various grades is only very narrow. In a modern, well-equipped coffee-roasting establishment, the coffee is handled almost exclusively by machinery, being fed into the cylinder from hoppers, emptied into the cooler from the cylinder and from thence into the bins by drafts of air through tubes or pocket-elevators, so that the coffee is scarcely once handled during the entire process.

The entire art of coffee roasting may be summed up in the following sequence: (1) Starting the machinery in motion. (2) Starting a brisk fire with enough coal for a single roast. (3) Putting in the coffee before the cylinder becomes too hot. (4) Opening the draft and keeping up a brisk fire during what is termed the steaming period. (5) When the beans begin to crackle and the steam changes into an aromatic vapor, rake the fire well, put on sufficient coal to make the next roast and shut off the draft. (6) Empty the coffee from the cylinder into the cooler and cool off rapidly, then sift and pack. If a light color is required roast quickly, if a dark, slowly. The exact time for a perfect roast under these rules depend to a great extent on the size of the cylinder, the quantity of coffee to be roasted, the amount of heat and the color desired, the average ranging from 30 to 40 minutes. The addition of a little water to the coffee when it begins to crackle in the cylinder, will cause the beans to swell up, liberate the chaff and make the process safer by extinguishing any sparks that may by accident occur in the cylinder. It also preserves the aroma longer to some extent when used in moderation, but will not, as is sometimes claimed, protect it from atmospheric influences, but on the contrary makes it more liable to such influences, particularly when used in excess.

When the beans begin to crackle the revolutions of the cylinder are increased for a short time in order to prevent them from scorching or burning, a bluish vapor is emitted at the same time, which indicates that the coffee is nearly if not quite roasted. At this stage the operator pours on the coffee a quantity of water to prevent it from burning, the rapid evaporation from which reduces the intense heat and causes the beans to burst open and swell up to about double in size. The use of a little lard at this juncture will impart to the beans a smoother, glossier and more attractive appearance. The addition of water in the roasting of coffee is not, as is generally supposed, intended to increase its weight--unless when used to excess--as the intense heat converts it into steam which rapidly passes off in the air, many old roasters contending that coffee cannot be properly roasted without the use of some water. In the proper roasting of coffee a strong, well-distributed heat extending the entire length of the cylinder is imperative. The cylinder should never be allowed to lie empty over the fire for any length of time or become too hot before the coffee is put in, as the beans will become mottled or “specked” if poured in while in that condition, thus detracting from the appearance and value of the roasted coffee.

An experienced roaster can readily discern when the coffee is properly roasted, by the light bluish vapor arising from the coffee, as well as by the smell of the aromatic principle developed as it evaporates from the cylinder at this stage of the operation, without even once examining it during the process. A perfect “light roast” should be free from specks and other blemishes, of a cinnamon-brown color, even, uniform and oily in appearance, much depending on the amount of this latter property developed in the process, imparting as it does a pleasanter and more agreeable aroma as the quantity is increased, making the liquor blander and more mellow in the cup. While a perfect high or “dark roast” when required should be of a deep chestnut or chocolate-brown color, oily and free from all burnt or scorched beans, as the latter, no matter how few the number, invariably spoil the flavor of the coffee in the infusion, irrespective of its fineness or value. Over-roasting dissipates the active principle (Caffeine) to which the coffee owes its refreshing and stimulating properties while under-roasting imparts to the infusion a raw, uncooked, grassy or astringent flavor by not properly developing it. So that the finest grades of coffee when imperfectly roasted--that is, be under or overdone--yield an inferior liquor to the poorer grades when properly roasted. As stated before, coffee contains a crystaline substance termed caffeine (identical with the theine of tea), which is volatile in its nature, and every care must be taken to retain this principle in the coffee, for which reason the beans should be roasted only until they are of a pale-brown color; again, if they are roasted too dark this essential property is destroyed.

The proper cooling of coffee after roasting is also an operation of great importance. If the coffee has been properly roasted and the beans well developed, it must be cooled quickly to prevent them from becoming too dark-colored or mottled in appearance. When the coffee has been cooled and cleaned it is then packed, the operations of roasting, cooling and rebagging occupying altogether about one hour.

In France and other European countries it is the custom to roast coffee in small quantities, so that the whole “charge” is well under the control of the operator during the process, while in this country large roasts are the rule, in dealing with which much difficulty is experienced in producing uniform torrefaction as well as in stopping the process at the proper moment. A novel method for roasting coffee in use in France is to put it in an iron globe, suspended over a brisk fire, and containing a tubular shaft perforated with holes smaller than the beans, through which passes the vapor generated from the coffee in the process of roasting and issuing out of either end of the shaft or axis of the globe. As these openings are small, but a limited amount of the vapor escapes, thus confining the aroma within the globe and securing the retention of the volatile or essential element of the coffee to a greater degree than is possible by the cylindrical method of roasting. When the globe is filled and suspended over the fire an iron cap is placed over it so as to completely surround it, but leaving an intervening space between it of about three inches, the object of which is to secure the full power of the heat, which being so confined circulates completely around the globe, the retention of the vapor under this high pressure preserving to a still greater degree the aroma of the coffee. The application of the heat by this method is very uniform, while the motion of the globe distributes the beans equally about the interior and thus removes any possible chance of scorching.

The roasting process also usually develops in many coffees more or less whitish beans, technically termed “quakers” but more properly “blights,” being in reality blighted or immature beans, which, having ripened to an extent on the tree and after obtaining a certain growth cease to draw further nutriment from it, thus failing to develop into healthy fruit. These peculiar beans detract considerably from the value of the coffee, and cannot always be detected in the natural state except by experts and others accustomed to the constant handling of raw coffee, but in the roasted condition their real character is unmistakably shown, presenting as they do a yellowish-white color, totally devoid of the moisture, oil and flavor so characteristic of the healthy bean. They exist to a much greater extent in some varieties more than others, most notably in lowland and coast-grown coffees--in mild grades more than strong--the only kinds most unaffected being mountain-grown and “washed” coffees, the blighted beans in the latter rising to the surface in the process of washing and carried off by the water. Some authorities contend that these “blights” or “quakers” in coffee instead of being, as might be naturally expected, detrimental or injurious to its drinking qualities really improve it by softening or mellowing what may otherwise prove to be a harsh or astringent flavor, thereby rendering it smoother and more palatable. Such a claim is simply preposterous, as the said beans are entirely devoid of any of the properties distinguishing coffee, possessing neither caffeine or caffeone, the two principal constituents of coffee, and an infusion prepared exclusively of “quakers” will be found to resemble more closely, in flavor and aroma, a decoction made from roasted peanuts than anything else it may be likened to.

Raw coffees are distinguished in commerce by the names of the countries, districts, localities, plantations in which they are grown or from the ports of export, and it is found that the produce of each particular country and respective district maintains a fairly constant and distinctive flavor and character of its own. While in the roasted state this distinctive character disappears, the process of roasting largely destroying these distinguishing features of raw or green coffee, making it very difficult for any but experts to determine from its appearance when once roasted its kind or origin. After coffee has been once roasted it should be kept in air-tight bins and sold or used as fresh-roasted as possible, as after the process the aroma constantly escapes, thereby losing its strength and fragrance rapidly on exposure to the oxydizing influences of the atmosphere. Neither should it be exposed in damp or humid weather, as it constantly absorbs moisture which makes it tough and difficult to grind, or placed in the vicinity of any foul or foreign odors, the porous and sensitive nature of the roasted bean making it liable to absorb such flavors, for which reason wooden and freshly-painted bins should never be used to hold roasted coffee, as it readily absorbs the wood and paint flavors, which become very pronounced in the infusion.

GLAZING.

It has been the custom for some years back to coat or glaze coffee with certain gluey or starchy compounds, ostensibly to protect the beans from the oxydizing influences of the atmosphere, preserve the aroma and clarify the liquor in preparation, each roaster and dealer having a different compound for the purpose. It is most generally composed of various glues, moss and other starchy substances and is usually prepared by placing the materials composing the compound in a cask, vat or tank filled with boiling water conveyed through pipes or by injecting steam, thoroughly stirring it at the same time until it is mixed to the requisite consistency. After the solution is prepared it is applied to the coffee while hot, generally in the cylinder while revolving, which diffuses the material and imparts an even and uniform coating to the coffee, adhering and hardening as it cools. But the claims made by roasters and others who coat or glaze coffee, that large quantities of eggs are used exclusively in the preparation of the glazing compound is simply absurd, as is also the claim that it is resorted to for the purpose of closing the pores, to protect and retain the aroma and for self-settling purposes. The real object being to conceal defects, disguise low grades and damaged coffees, as well as to add weight and color to light, chaffy and “quakery” coffees, the process adding all the way from 5 to 10 per cent. to the weight, according to the nature of the coffee and the character of the substance used; light, chaffy-bean coffees absorbing more of the material than the hard and solid ones, while the softer and rougher the bean the more it improves in appearance by the process.

What is known as the “Egg-glaze” is prepared from eggs alone, mashed and applied after the coffee has been first cooled, and then baked on by means of a hot blast, when it forms a hard, transparent shell, protecting the coffee until it is ground and ready for use; and also serving to clarify the liquor in the pot after infusion. Another composed of one part gum arabic dissolved in water, to which is added four parts starch, with sufficient water to make it limped, the whole being boiled for upwards of twenty minutes, and which is best accomplished by inserting a small pipe of live steam from the boiler into the compound until it is reduced to the consistency of cream; then, after stirring well, it is poured on the coffee while in the cylinder as it revolves, or it may be spread over it while in the cooler, if proper care be taken to diffuse it well. Still another excellent compound for glazing coffee is prepared from one part Irish moss, one part gelatine, one part isinglass, one ounce sugar and two dozen eggs, the first three ingredients being first boiled in water, then strained and applied as in foregoing formula. For the purpose of imparting a lustrous aspect to roasted coffee, a liquid has recently been invented, the composition of which is so far unknown. It has a specific gravity of 0.868 at 15 degrees, burning with a sooty flame and leaving no fixed residue. It absorbs no iodine when treated, and is but little affected by chromic acid or concentrated sulphuric acid, taking only a slight color when treated with the latter. It is clear and oily in appearance, but entirely free from color, taste, or smell, and mixes in all proportions with petroleum, from which fact it would appear to be nothing more than a highly purified petroleum oil, in which case it must be classed among the illegitimate additions to roasted coffee.

GRINDING.

The process of grinding the roasted bean is also one that requires more attention than is generally bestowed on it. Coarse-ground coffees require protracted boiling in order to extract its full strength, and too much boiling is fatal to the production of good coffee in the cup. But, on the other hand, it may be ground too fine, so that just to what degree of fineness it should be ground depends in a great measure on the method of preparing it for use.